1. Field of the Invention
The invention relates to differential gearing for an energy generation plant, in particular for a wind power station, with three drives and outputs, a first drive being connected to a drive shaft of the energy generation plant, one output being connected to a generator that can be connected to a grid, and a second drive being connected to an electrical machine as a differential drive.
The invention furthermore relates to a method for operating differential gearing for an energy generation plant, in particular for a wind power station, with three drives and outputs, a first drive being connected to a drive shaft of the energy generation plant, one output being connected to a generator that can be connected to a grid, and a second drive being connected to an electrical machine as a differential drive.
2. Description of the Related Art
Wind power stations are becoming increasingly important as electrical generating plants. For this reason, the percentage of power generation by wind is continuously increasing. This in turn dictates, on the one hand, new standards with respect to current quality, and, on the other hand, a trend toward still larger wind power stations. At the same time, a trend is recognizable toward offshore wind power stations that requires station sizes of at least 5 MW installed power. Due to the high costs for infrastructure and maintenance or servicing of wind power stations in the offshore region, here, both efficiency and also the availability of the stations acquire special importance.
The necessity of a variable rotor speed is common to all plants, on the one hand, for increasing the aerodynamic efficiency in the partial load range, and, on the other hand, for controlling the torque in the drive line of the wind power station, the latter for purposes of speed control of the rotor in combination with rotor blade adjustment. Currently, for the most part, wind power stations are used that meet this requirement by using variable-speed generator designs in the form of so-called double-supplied three-phase machines or synchronous generators in concert with frequency converters. These designs, however, have the disadvantage that (a) the electrical behavior of the wind power stations in the case of a grid problem only conditionally meets the requirements of the electricity supply company, (b) the wind power stations can only be connected to the medium voltage grid by means of a transformer station, and (c) the frequency converters necessary for the variable speed are very powerful and therefore a source of efficiency losses.
These problems can be solved by using separately excited medium voltage synchronous generators. Here, however, alternative designs are needed to meet the requirement for variable rotor speed or torque control in the drive line of the wind power station. One possibility is the use of differential gearing that allows a variable speed of the rotor of the wind power station by changing the transmission ratio at constant generator speed.
WO2004/109157 A1 shows a complex, hydrostatic “multipath” concept with several parallel differential stages and several switchable clutches, as a result of which it is possible to switch between the individual paths. With the illustrated technical design, the power and thus the losses of the hydrostatics can be reduced. One major disadvantage is, however, the complex structure of the entire unit. Moreover, the switching between the individual stages constitutes a problem in the control of the wind power station.
EP 1283359 A1 shows 1-stage differential gearing with an electrical differential drive, with a special three-phase machine that is positioned coaxially around the input shaft, with low nominal speed and high nominal output—relative to the implemented speed range.
The disadvantages of known embodiments are, on the one hand, high losses in the differential drive, and, on the other hand, for concepts that solve this problem, complex mechanisms or special electrical machine construction and thus high costs. In hydrostatic designs, moreover, the service life of the pumps used is a problem, and high cost is necessary when adapted to extreme environmental conditions. In general, it can be maintained that the chosen nominal speed ranges are either too small for the correction of extreme loads or too large for optimum energy yield of the wind power station.